Various methods, systems and apparatus relating to the present invention are disclosed in the following co-pending applications filed by the applicant or assignee of the present invention:
PCT/AU00/00594, PCT/AU00/00595, PCT/AU00/00596, PCT/AU00/00597,
PCT/AU00/00598, PCT/AU00/00516 and PCT/AU00/00517.
The disclosures of these co-pending applications are incorporated herein by cross-reference.
The present invention relates to printed media production and in particular ink jet printers.
Ink jet printers are a well-known and widely used form of printed media production. Ink is fed to an array of digitally controlled nozzles on a printhead. As the print head passes over the media, ink is ejected from the array of nozzles to produce an image on the media.
Printer performance depends on factors such as operating cost, print quality, operating speed and ease of use. The mass, frequency and velocity of individual ink drops ejected from the nozzles will affect these performance parameters.
Recently, the array of nozzles has been formed using microelectromechanical systems (MEMS) technology, which have mechanical structures with sub-micron thicknesses. This allows the production of printheads that can rapidly eject ink droplets sized in the picoliter (xc3x9710xe2x88x9212 liter) range.
While the microscopic structures of these printheads can provide high speeds and good print quality at relatively low costs, their size makes the nozzles extremely fragile and vulnerable to damage from the slightest contact with fingers, dust or the media substrate. This can make the printheads impractical for many applications where a certain level of robustness is necessary. Furthermore, a damaged nozzle may fail to eject the ink being fed to it. As ink builds up and beads on the exterior of the nozzle, the ejection of ink from surrounding nozzles may be affected and/or the damaged nozzle will simply leak ink onto the printed substrate. Both situations are detrimental to print quality.
Accordingly, the present invention provides a printhead for an ink jet printer, the printhead including:
an array of nozzles for ejecting ink onto media to be printed;
an apertured containment formation positioned between the nozzle and the media when the printhead is in use; such that,
ink fed to the nozzle is isolated from at least some of the other nozzles in the array while allowing ink correctly ejected from the nozzle to pass through an aperture in the containment formation to print the media.
In this specification the term xe2x80x9cnozzlexe2x80x9d is to be understood as an element defining an opening and not the opening itself.
Preferably, each nozzle in the array has a respective containment formation to isolate it from all the other nozzles in the array. However, some forms of the invention may have a containment formation configured for isolating predetermined groups of nozzles from the other nozzles in the array.
In a further preferred form, the containment formation is an apertured nozzle guard positioned on the printhead such that it extends over the exterior of the nozzles to inhibit damaging contact with the nozzles while permitting ink ejected from the nozzles to pass through the apertures and onto the substrate to be printed.
In some embodiments, the nozzle guard covers the exterior of the nozzles and the apertures form an array of passages in registration with the array of nozzles so as not to impede the normal trajectory of the ink ejected from each nozzle, and
the nozzle guard further includes containment walls extending from the array of passages to the exterior of each of the nozzles to form a ink containment chamber enclosing each nozzle. In a further preferred form, the nozzle guard is formed from silicon.
In one particularly preferred form, each containment chamber has ink detection means which actuates upon a predetermined level of ink within the chamber and provides feedback for a fault tolerance facility to adjust the operation of other nozzles with the array to compensate for the damaged nozzle. In some forms of this embodiment, the printer stops supplying ink to the damaged nozzle in response to the ink detection means.
An ink jet printer printhead according to the present invention, isolates any ink leakage such that it is contained to a single nozzle or group of nozzles. By containing the ink flooding, the adjacent nozzles can compensate to maintain print quality.
The containment walls necessarily use up a proportion of the surface area of the printhead, and this adversely affects the nozzle packing density. The extra printhead chip area required can add 20% to the costs of manufacturing the chip. However, in situations where the nozzle manufacture is unreliable, the present invention will effectively account for a relatively high nozzle defect rate.
The nozzle guard may further include fluid inlet openings for directing fluid through the passages, to inhibit the build up of foreign particles on the nozzle array.
The nozzle guard may include a support means for supporting the nozzle shield on the printhead. The support means may be integrally formed and comprise a pair of spaced support elements one being arranged at each end of the guard.
In this embodiment, the fluid inlet openings may be arranged in one of the support elements.
It will be appreciated that, when air is directed through the openings, over the nozzle array and out through the passages, the build up of foreign particles on the nozzle array is inhibited.
The fluid inlet openings may be arranged in the support element remote from a bond pad of the nozzle array.
By providing a nozzle guard for the printhead, the nozzle structures can be protected from being touched or bumped against most other surfaces. To optimize the protection provided, the guard forms a flat shield covering the exterior side of the nozzles wherein the shield has an array of passages big enough to allow the ejection of ink droplets but small enough to prevent inadvertent contact or the ingress of most dust particles. By forming the shield from silicon, its coefficient of thermal expansion substantially matches that of the nozzle array. This will help to prevent the array of passages in the shield from falling out of register with the nozzle array. Using silicon also allows the shield to be accurately micromachined using MEMS techniques. Furthermore, silicon is very strong and substantially non-deformable.